Test unit for testing the frequency characteristic of a transmitter

ABSTRACT

A test unit for testing the frequency characteristics of one or more components of a transmitter of modulated signals. The test unit includes a data source for generating a test pattern of data. A test unit output is connected to the data source and connectable to an input of one or more of the components, for inputting the test pattern of data to the one or more components. The test unit includes a memory in which a first predetermined data sequence and a second predetermined data sequence are stored. The data source is connected with an data input to the memory, and the data source is arranged to generating the test pattern of data including the predetermined data sequences. When a modulated signal is generated in accordance with the test pattern of data will include a first signal part with a first frequency spectrum caused by the first predetermined data sequence and a second signal part after the first signal part, which second signal part has a second frequency spectrum caused by the second predetermined data sequence.

FIELD OF THE INVENTION

This invention relates to a test unit, a data carrier, a transmittercomponent, a transmitter unit, a method for testing, a method foroptimising component of a transmitter, and a computer program product.

BACKGROUND OF THE INVENTION

In the art of data communication, it is known to test a transmitter unitfor the power outputted in the different frequency bands. For instance,3GPP standard document 3G TS 51.010-1 provides specification for testingwhether or not an output RF spectrum (ORFS) of an Enhanced Data ratesfor Global Evolution (EDGE) transceiver complies with the requirementsset by the part of the 3G standards relating to EDGE telecommunicationsystems.

Known methods for testing whether or not the output RF spectrum complieswith the EDGE standard include observing the output power spectrum overa couple of hundreds of bursts. The burst include a random bit pattern.The bursts are generated by generating data packets incorporating therandom bit pattern in the data packet and generating a phase shiftkeying (PSK) modulated signal according to the generated data packet.The PSK modulated signal is subsequently inputted to the transmitterunit to be tested. The RF spectrum of the signals outputted by thetransmitter unit is monitored to measure whether the ORFS complies withthe EDGE standards.

However, a general disadvantage of the known test methods is that theyare time consuming since hundreds of burst are used to get an accurateand stable measurement. Furthermore, the known test methods do not givea clear insight in the characteristics of the tested components.

SUMMARY OF THE INVENTION

The present invention provides a test unit, a data carrier, atransmitter component, a transmitter unit, a method for testing, amethod for optimising component of a transmitter, and a computer programproduct as described in the accompanying claims.

Specific embodiments of the invention are set forth in the dependentclaims.

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details, aspects and embodiments will be described, by way ofexample only, with reference to the drawings.

FIG. 1 shows a block diagram of a first example of an embodiment of atest unit.

FIG. 2 shows a block diagram of an example of an embodiment of amodulator.

FIG. 3 shows an example of a data packet.

FIG. 4 shows a block diagram of a second example of an embodiment of atest unit.

FIG. 5 shows a block diagram of a third example of an embodiment of atest unit.

FIGS. 6 and 7 show block diagrams of examples of embodiments of a datasource.

FIGS. 8A-C illustrate phase shift keying with a phase offset.

FIGS. 9A and B show examples of frequency spectra obtained with anexample of a method for testing frequency behaviour.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the example of FIG. 1, an example of a test unit 1 isshown. The test unit 1 may be used to test the frequency characteristicsof one or more components 21,22 of a transmitter 2. The test unit 1 mayfor instance be used to determine the frequency spectrum of thetransmitter 2 or of the components 21,22. The test unit 1 may forexample generate a test signal S_(test) which can be inputted in thetransmitter 2 or in one or more transmitter components 21,22. The testunit 1 may be part of a testing arrangement which further includes areceiving unit 3. The receiving unit 3 may for example receive amodulated signal S_(RF) outputted by the transmitter 2 (or by one ormore components of the transmitter 2) in response to the test signalS_(test) and determine the frequency spectrum of the modulated signalS_(RF).

As shown in FIG. 1, the test unit 1 may include a data source 11 whichis connectable via a test unit output 14 to one or more components 21,22of a transmitter 2 of modulated signals. The data source 11 may generatea test pattern T of data. The test pattern T may include a sequence ofsymbols. In the example of FIG. 1, decimal symbols are shown, howeverthe symbols may also be (sequences of) binary symbols, hexadecimalsymbols or other types of data.

A test signal S_(test), for example a modulated signal S_(RF), may begenerated in accordance with the test pattern T. For example, abase-band test signal S_(base) corresponding to the test pattern T maybe generated. For instance, the test pattern T may consist of binarynumbers and a digital base-band test signal S_(base) may be generated inaccordance with the order and binary values in the test pattern T. Thedigital signal S_(base) may then be modulated to generate a modulatedtest signal S_(RF). Also, for example, the modulated signal S_(RF) maybe generated by controlling one or more modulation parameters inaccordance with the test pattern T. For instance, the test pattern T mayinclude a sequence of (decimal) symbols and a parameter of the modulatedsignal S_(RF) may be set to a value corresponding to the respectivesymbol. The modulation parameter may for example be the phase φ, theamplitude A, or the frequency f of the signal S_(test). For example, thephase φ of a periodic signal may be varied in accordance with the symbolin the test pattern T, as is explained below in more detail, and theperiodic signal may be mixed with another signal to obtain a modulatedsignal.

As shown in the example of FIG. 1, the data source 11 may for instancegenerate the test pattern T and output the test pattern T at the testoutput 14. The test pattern T may be inputted to an input of thetransmitter component(s) to be tested, for instance to an input 20 ofthe transmitter 2. As shown in the example of FIG. 1, for instance, thetransmitter 2 may include a modulation unit 21 and a power amplifier 22.The modulation unit 21 may for example be connected with an input 210 tothe transmitter input 20. An output 219 of the modulation unit 21 may beconnected to an input 220 of the power amplifier 22. The output 221 ofthe power amplifier 22 may be connected to an output 23 of thetransmitter 2. As shown in FIG. 1, the transmitter 2 may be connectedwith the transmitter output 23 to other devices or components, such asan antenna 4.

The transmitter 2 may generate a test signal S_(test), such as amodulated test signal S_(RF), from the test pattern T. However, as isexplained below in more detail with reference to FIG. 4, it is alsopossible that the test unit 1 itself generates a test signal S_(test)suitable to be inputted in the component 21,22 to be tested from thetest pattern T. The test unit 1 may then input the test signal S_(test)into the respective component 21,22 of the transmitter 2.

The test unit 1 may further be implemented as a part of atelecommunication system and for example be integrated in an integratedcircuit package. As shown in FIG. 5, for instance the test unit 11 maybe implemented in a communication device 100, for example to test thetransmitting components 21,22 in the communication device 100.

For instance, separate components 21,22 of a transmitting unit 2 may betested. The test unit 1 itself may include one or more transmittercomponents 21,22. The transmitter components in the test unit 1 may becomponents which would be positioned in a transmitting unit, in a signalprocessing direction, upstream of the component to be tested and whichcan generate the signal to be inputted in the transmitter component tobe tested. For example, as shown in FIG. 4, the test unit 1 may includea modulation unit 21 with a modulation output 219 which is connected tothe test unit output 14 and, as indicated with the dashed line in FIG.4, is connectable to an amplifier input 220 of a separate poweramplifier 22. The modulation unit 21 in the test unit 1 may generate amodulated test signal S_(RF) which can be inputted in the poweramplifier 22, to test the characteristics of the power amplifier 22.

As shown in FIG. 1, the test unit 1 may include a memory 12 in which afirst predetermined data sequence T1 and a second predetermined datasequence T2 are stored. The data source 11 may be connected with an datainput 110 to the memory 12. The data source 11 may include thepredetermined data sequences T1,T2 in the test pattern T (in FIG. 1, thepredetermined data sequences T1,T2 are shown in bold face andunderlined, for sake of clarity).

As is explained below in more detail, the first predetermined datasequence T1 may cause the modulated signal S_(RF) to have, during afirst period of time, a first signal part S1 with a first frequencyspectrum and the second predetermined data sequence T2 may cause, duringa second period of time different from the first period of time, themodulated signal S_(RF) to have a second signal part S2 with a secondfrequency spectrum. Thereby, the effect of the component 21,22 to betested on the spectrum of the modulated signal can be determined in arelatively simple manner.

For instance, the part of the signal outputted by the component 21,22which corresponds to the first signal part S1 may be compared with afirst criterion and the part of the signal outputted by the component21,22 which corresponds to the second signal part S2 may be comparedwith the second criterion, Also, for example, a comparison may be madebetween the part of the signal outputted by the component 21,22 whichcorresponds to the first signal part S1 with the first signal part S1.Furthermore, a comparison may be made between the part of the signaloutputted by the component 21,22 which corresponds to the first signalpart S1 part of the signal outputted by the component 21,22 whichcorresponds to the second signal part S2.

Furthermore, the time required to determine the effect of the component21,22 to be tested on the spectrum of the modulated signal can berelatively short since, by means of the first and second predetermineddata sequence T1,T2, the desired test conditions, may be made to occur.The first and second predetermined data sequence T1,T2 may for instancebe selected in such a manner that a desired amount of difference in therelevant aspects of the frequency spectrum may be obtained. For example,as is explained below in more detail, the first predetermined datasequence T1 may cause a modulated signal spectrum with an upper sideband (rejected side band) which is much stronger than the lower sideband at a desired frequency of interest and the second predetermineddata sequence T2 may cause in the same manner a modulated signalspectrum with a lower side band which is much stronger than the upperside band (rejected side band), thus enabling to test extreme cases ofdistortion of the RF frequency spectrum caused by modulated signal(modulation switching Output RF spectrum)

The test unit 1 may for instance be used to optimise the frequencybehaviour of one or more components 21,22 of a transmitter 2 ofmodulated signals. For example, the test pattern T may be used togenerate the modulated test signal S_(RF) and cause the testedcomponent(s) of the transmitter 2 to output a signal. As shown in FIG.1, for instance, the signal may be outputted by the transmitter 2 via anantenna 4. A receiving unit 3 may receive the outputted signal outputtedby the component in response to inputting the test pattern in thecomponent. The receiving unit 3 may for example determine frequencycomponents in the received signal caused by first signal part S1 and thesecond signal part S2 respectively. For instance, the receiving unit 3may determine a first frequency component during a first period of timecorresponding to the first signal part S1 and determine a secondfrequency component during a second period of time corresponding to thesecond signal part S2. The determined frequency components may then becompared with one or more criteria and one or more parameters of thecomponent 21,22 may be adjusted when the comparison meets an adjustcriterion. The parameters may for example include one or more of: thequiescent currents of one or more RF transistors of a power amplifier,pre-distortion coefficients and/or settings of a transmitter, or anyother suitable parameters. The parameter(s) may for example be adjustedby minimizing the rejected upper side band and/or lower side band of RFspectrum signal.

As for instance shown in FIG. 9A, for example, the modulated signalspectrum caused by the first predetermined data sequence T1 may forexample have peaks in the frequency spectrum at positions f₀±n*f_(m),n=0,±1,±2, . . . and the peaks at f₀−n*f_(m) may be higher than thepeaks at f₀+n*f_(m). As shown in FIG. 9B, for instance, the modulatedsignal spectrum caused by the first predetermined data sequence T1 mayfor example have peaks in the frequency spectrum at positionsf₀±n*f_(m), n=±1,±2, . . . and the peaks at f₀−n*f_(m) may be lower thanthe peaks at f₀+n*f_(m). In FIGS. 9A and 9B an EDGE burst signal hasbeen outputted with a centre frequency f₀ of about 118 kHz and f_(m) of270 kHz using first and second data patterns in the data part of theEDGE burst corresponding to the sequences listed in Table 4. As shown inFIGS. 9A and 9B by inserting a suitable data pattern, for instance thefrequency spectrum of the signal may be adjusted and accordingly, forexample, the maximum intensity in a certain frequency band may bedetermined. For instance, the intensity of the frequency band atf₀±2*f_(m) may be determined and compared to a threshold. For example,the EDGE standard specifies a limit to the intensity at this frequencyband, which in EDGE modulated signal lies at f_(modulation)±400 kHz withf_(modulation) being the carrier frequency. Thus, by adjusting theparameters of the components 20,21 until this frequency band meets thislimit, the components 20,21 can be made to comply with the requirementsof the EDGE standard.

As shown in FIG. 1, the receiving unit 3 may be connectable to one ormore (?) of the components 21,22 in order to receive a signal outputtedby the respective component 21,22 in response to inputting the testpattern T (or the test signal S_(test)) in the component. The receivingunit 3 may, as shown in FIG. 1, for example include an antenna 31 forreceiving a wireless signal transmitted by the transmitter 2. Theantenna 31 may be connected to a receiver (RX) which can, for example,convert the received, modulated signal into a base-band signal ordetermine the frequency components present in the received signal. Thereceiver RX 32 may for example include a spectrum analyser or anycommunication test equipment. The RX 32 may for example determine thefrequency components in a frequency range with a lower limit atfrequency f₁ and with an upper limit at frequency f₂, which frequencyrange includes the centre frequency f₀ of the received, modulatedsignal. f₁ may for example be about 600 kHz lower than the carrierfrequency, such as for instance 550 kHz, such as 541.6 kHz for instance.F₂ may for example be about 600 kHz higher than the centre frequency f₀,such as for instance 550 kHz, such as 541.6 kHz higher for instance. Thecentre frequency f₀ may for example be shifted relative to the carrierfrequency used to modulate the signal at the transmission side. Thecentre frequency may for example be in the range between 100 kHz and 150kHz, f₀ instance between 110 kHz and 125 kHz, such as approximately 118kHz. As explained above, experimental results have been obtained withf₀=118.67 KHz and f₁=f₀−270.83 KHz f₂=f₀+270.83 KHz. For instance, fromthe part of the received signal corresponding to the first signal partS1 (and hence the first predetermined sequence T1) a first frequencyspectrum within the frequency band may be determined. From the part ofthe received signal corresponding to the second signal part S2 (andhence the second predetermined sequence T2), for instance, a secondfrequency spectrum within the frequency range may be determined. Fromthe first and second frequency spectra, one or more parameters may becompared. For instance, the first and second frequency spectra may becompared with each other in a sub range which lies between the carrierfrequency f₀ and the upper limit f₂ of the frequency range and/or a subrange which lies between the carrier frequency f₀ and the lower limit f₁of the frequency range.

The test pattern T may be inputted to the transmitter 2 in any suitablemanner and the data source 11 may be any type of data source suitablefor the specific implementation. For instance, the data source 11 maygenerate data packets with a payload in which the predetermined datasequences T1,T2 are included, or generates the sequences T1 and/or T2 ina continuous manner. The data packets may for example comply with a datacommunication standard, and may for instance be EDGE bursts. Referringto FIG. 3, a structure of an example of a data packet 400 is shown. Asshown in this example, the data packet 400, in which the first andsecond data sequences T1,T2 are included, may comply with the definitionof a normal data packet, also referred to in the art as a ‘burst’, asdefined in the EDGE standard. The data source 11 may also have a burstmode for outputting a sequence of one or more bursts and may output thefirst and second signal parts S1,S2 in the same burst.

As shown, the data packet 400 may include an initial tail 401, a firstdata part 402, a training sequence 403, a second data part 404, a finaltail 405 and a guard period 406. Each segment 401-406 may for examplehave the number of symbols as listed in Table 1.

TABLE 1 part symbols initial tail 401 3 first data part 402 58 trainingsequence 403 26 second data part 404 58 final tail 405 3 guard period406 8

The initial tail 401 ramp-up of the test signal outputted by thetransmitter 2. The training sequence 403 may be used to determinecharacteristics of the communication channel. The final tail 405 mayinclude data used in error correction, The guard period 406 is usedduring the gradual reduction (ramp-down) of the test signal. The firstand second data parts 402,404 may include user data, for example dataoutputted by a signal processor 112.

The first and second data parts 402,404 may for instance include thetest pattern T. For example, the first predetermined data sequence T1may be included in the first data part 402 and the second predetermineddata sequence T2 may be included in the second data part 404. An exampleof a suitable sequence of symbols of a EDGE burst is listed in Table 2,in which the predetermined sequences T1,T2 are shown in bold typefaceand underlined. It will, however, be apparent that other sequences mayalso be used.

TABLE 2 tail 401 7 7 7 data 402 6 5 1 2 5 7 0 4 3 6 4 1 0 5 6 3 0 5 1 23 6 1 6 1 6 1 6 1 6 1 6 1 6 5 1 4 4 7 7 2 2 1 1 4 4 7 7 4 1 2 6 6 1 1 33 4 test 403 7 7 1 7 7 1 7 1 1 1 7 7 7 7 1 7 7 7 1 7 7 1 7 1 1 1 data404 4 1 2 7 3 2 0 1 5 4 6 4 1 3 1 3 3 0 0 7 0 7 7 2 2 6 2 6 6 3 3 4 3 44 7 7 6 5 1 2 5 7 0 4 3 6 4 1 0 5 6 3 0 5 1 0 3 tail 405 7 7 7

As shown in table 2, the test pattern, formed in the example of Table 2by the data in the first and second data parts 402,404, may include, inaddition to the predetermined sequences T1,T2 additional data The testpattern T of data may for example include compensating data whichcompensate a parameter of the test signal S_(test) for an effect on theparameter caused by the first predetermined data sequence T1 and/or bythe second predetermined data sequence T2. For instance, thecompensation data may be selected such that the power level of themodulated signal S_(RF) is compensated, relative to a power level of areference modulated signal. The compensation data may for example be apseudo random sequence (PN15 for example). conformed to apeak-to-average and a peak-to-minimum of an EDGE modulated signal.

The first predetermined data sequence T1 and the second predetermineddata sequence T2 may differ in any suitable manner. For example, thefirst predetermined data sequence T1 and the second predetermined datasequence T2 may cause in the modulated signal S_(RF) a first signal partS1 and a second signal part S2 respectively, which differ in thefrequency components in any suitable manner. For example, the firstsignal part S1 may have one or more frequency components with afrequency f₊ above a carrier frequency f₀ which have a higher intensitythan corresponding frequency component(s) f₊ in the second signal partS2. The second signal part S2 may have one or more frequency componentswith a frequency f below the carrier frequency f₀ with a higherintensity than a corresponding frequency component in the first signalpart S1.

The first signal part S1 and the second signal part S2 may for exampleeach have the frequency spectrum of a single-sideband modulated signal.The frequency component of the first signal part S1 may for example bethe first upper side band of the modulated signal S_(rf) above thecarrier frequency f₀ and/or the frequency component of the second signalpart S2 may be the first lower side band of the modulated signal S_(RF),that is the first frequency band below the band of the carrier frequencyf₀.

The test unit 1 may be implemented in any manner suitable for thespecific implementation. The test unit 1 may for instance include one ormore units which perform different functions. As shown in FIG. 6, forinstance, the test unit 1 may include a signal processor 112 whichgenerates base-band data and a modem 113 which may perform data codingand/or modulation and/or burst formation and/or burst timing, forexample. The modem 113 may for example be positioned, in a signalprocessing direction, downstream of the signal processor 111. The modem113 may perform transmission and/or reception related functions, such ascoding the base band data, in which the first and second data sequenceT1,T2, generated by the signal processor, generating data packets inwhich the base-band data is included the base-band data, controlling thetiming of the transmission of the data. The modem 113 may for examplecode the base-band data in which the first and second data sequenceT1,T2 are included, by performing one or more of channel coding, bitinterleaving, encryption, multiplexing, etc. As shown, the signalprocessor 112 may for example be connected to the memory 12 and generatedata in which the first and second predetermined data sequence areincluded. The signal processor 112 may output the base-band data to themodem 113. The modem 113 may generate one or more data packets 400 inwhich the predetermined data sequences T1,T2 are included, for examplein the payload of one or more of the data packets

As shown in FIG. 7, it is also possible that the modem 113 is connectedto the memory 12. The modem 113 may include the first and secondpredetermined data sequence T1,T2 in the data packet, for example byinserting at the position of the user data in the data packet 400. Forinstance, as is explained below, the modem 113 may insert the first andsecond predetermined data sequence T1, T2 in the first or second datapart 402,404 of an EDGE burst.

The predetermined data sequences T1,T2 may be any sequence suitable toobtain, after modulation, the desired different frequency components.The first predetermined data sequence T1 may for instance include two ormore different symbols and a transition between two successive symbolsmay correspond in the first signal part S1 with a first phase shift φ₁in a first direction and the second predetermined data sequence T2 mayinclude two or more different symbols. A transition between a symbol toa following symbol may correspond to a second phase shift φ₂ in a seconddirection opposite to the first direction. The first and second phaseshift φ₁,φ₂ may for example be of the same magnitude but of oppositedirection, or be of different magnitudes.

The first predetermined data sequence T1 and the second predetermineddata sequence T2 may each include three, four, five or more symbols. Insuch a case, the first and second phase shift φ₁,φ₂ may have the samemagnitude for each transition from a symbol to a following symbol. Thefirst and second phase shifts φ₁, φ₂ may have any value suitable for thespecific implementation and be in the range of larger than zero andsmaller than 180 degrees. In case the test signal is a digital modulatedsignal, the sequences T1,T2 of symbols may be selected such that foreach transition the modulated signal has a phase shift as close to 180degrees as possible or instance, 3π/8-PSK the first and second phaseshifts φ₁, φ₂ may be ±157.5 degrees, with a suitable margin of error.The margin of error may for example be below the error threshold atwhich it is no longer possible to distinguish different symbols fromeach other.

The test signal S_(test) may be any type of modulated signal suitablefor the specific implementation. The test signal may for example be adigitally modulated signal, such as a phase shift keying modulatedsignal, an amplitude shift keying modulated signal or any other suitabletype of signal. The test unit 1 or the transmitter 2 may include amodulating unit 21. Referring to the example of FIG. 2, there is shown amodulating unit 21 which may be used in the transmitter 2 and/or thetest unit 1. The modulating unit 21 may modulate a signal inputted at aninput 210 to obtain a modulated signal and output the modulated signalat the output 219. The shown example of a modulating unit 21 is adigital modulation unit, more in particular a shift keying unit, andmore in particular a phase shift keying unit. The modulation unit 21 mayfor example be a source of m-PSK modulated signals with a phase offsetof pπ/q radians, and wherein m is an integer number and m, p and qsatisfy the relationship:

$\begin{matrix}{{{2{\pi\left( {\frac{n}{m} + \frac{p}{q}} \right)}} \neq {k\;\pi}},} & (1)\end{matrix}$

in which relation n is a positive integer number smaller or equal to m,and k is an integer number. M may for example be a power of 2, forexample 2³ and p/q may for example be 3/8. The signal source may forinstance be source of 8-PSK modulated signals with a 3π/8 offset, fromhereon referred to as 3π/8-PSK.

The modulating unit 21 may receive a sequence of binary signalsrepresenting the first and second predetermined data sequence. Referringto FIG. 2, an example of a modulation unit 21 is shown which canmodulate a signal according to a digital modulation scheme, in thisexample phase shift keying. The modulation unit 21 may, as shown,include an data input 210 at which a sequence of data may be inputted.The data input 210 may be connected to a mapping unit 211 which includesa (not shown) memory in which data representing a relationship betweendata and a modulation scheme is stored. The sequence of data received bythe modulation unit 21 may for example be a sequence of binary data.

The mapping unit 211 may split the incoming sequence of binary data in3-bit sequences and map the 3-bit sequences according to mappinginformation stored in a memory (not shown in FIG. 2). As shown in theexample of FIG. 2, the inputted sequence of binary data may for exampleinclude portions corresponding to the first and second predetermineddata sequence T1,T2. E.g. supposing that the mapping unit 211 uses aGray coding scheme and that the sequences 7214 and 70431625 arerespectively selected, the inputted sequence of binary data may forexample include respective corresponding portions 100,011,001,110 and100,000,110,010,001,101,011,111. The inputted sequences result in theoutputted RF signal having a first frequency characteristic during aperiod of time corresponding to the first sequence, e.g. 7214, and asecond frequency characteristic during a period of time corresponding tothe second sequence, e.g. 70431625.

The mapping unit 211 may for example include a table which maps a n-bitbinary sequences (n being an integer larger than or equal to 2) to adigital number. For instance, the table may map 3-bit sequences todecimal numbers q (e.g. integers in the ranged from 0 to 7). The tablemay further map the each of decimal numbers q to a specific digitalmodulation mode. For instance, the modulation scheme may be a phaseshift keying scheme and the table may map each of the decimal numbers qto a corresponding phase (or phase shift) φ_(q). For example, themodulation may be 8-PSK and the table may map each of the decimal numberq (q being an integer in the range from 0 to 7), to a correspondingphase φ_(q). The phases φ_(q) may for example be equally distributed ande.g. be spaced q*π/2^(n) radians. The modulating unit 21 may forexample, as shown in FIG. 2, include a table in which is listed whichsequence represents a certain symbol. For instance, the binary signalsmay be mapped to symbols using a Gray coding scheme. An example of a3-bit Gray coding mapping of symbols and binary signals is shown inTable 3, which further shows the phase associated with a symbol forapplication of the 3-bit mapping in 8-phase shift keying (8-PSK).However, it should be noted that the modulating unit 21 may modulate thesignal in another manner and may for example apply binary phase shiftkeying, quadrature phase shift keying or any other suitable kind ofmodulation.

TABLE 3 8PSK phase Modulation Bits symbol (radians) 111 7 0 011 3  π/4010 2  π/2 000 0 3π/4 001 1 π 101 5 5π/4 100 4 3π/2 110 6 7π/4

The mapping unit 211 outputs a signal with the phase φ_(q) defined bythe mapping information to a phase rotation unit 212. The phase rotationunit 212 may add a phase rotation to the outputted signal S_(test) (q),in order to shift the phase of the signal. For example, the phaserotation unit 212 may cause the signal outputted by the mapping unit 211to have an additional phase shift of φ_(offset).

The phase rotation unit 212 may for example add an additional phaseshift φ_(offset). The additional phase shift φ_(offset) may for examplechange with each transition to a following symbol q, and for example bemultiplied by an integer counter value which is increased for eachtransition. E.g. before a first transition the additional phase shiftφ_(offset) may be 0, after the first transition the additional phaseshift φ_(offset) may be a*π radians, after a second transition theadditional phase shift φ_(offset) may be 2*a*π radians, after a thirdtransition the additional phase shift φ_(offset) may be 3*a*π radians,etc.

The phase rotation unit 212 may output the phase rotated signalS(φ_(q)+φ_(offset)) to a filter 213. The filter 213 may modify the phaserotated signal S(φ_(q)+φ_(offset)) to have a desired frequency profile.For example, the filter 213 may be a Gaussian filter, such as alinearized Gaussian filter. For instance, the filter 213 may process thephase rotated signal S(φ_(q)+φ_(offset)) in order to limit the frequencycomponents in the phase rotated signal S(φ_(q)+φ_(offset)) to a certainbandwidth. As shown in FIG. 2, the filter 213 may be connected to one ormore mixers 214,215 and input the filtered signal S_(f) into the mixers214,215.

The mixers 214,215 may mix the filtered signal S_(f) with a localoscillator (LO) signal. For instance in the example of FIG. 2, themodulation unit 21 includes a local oscillator 216 which generates a LOsignal. The LO signal may for example have a base frequency which ishigher than the dominant frequency in the filtered signal S_(f). Themodulation unit 21 may for example generate an I/Q signal. In theexample of FIG. 2, for instance, the local oscillator 216 is connectedto a phase splitter 217. The phase splitter 217 may generate two or moresignals with the same frequency, but shifted in phase. For example, thephase splitter may generate a first signal LO(φ₁) with a first phase φ₁and a second signal LO(φ₂) with a second, different phase φ₂ atrespective outputs. The first phase φ₁ may for example differ π/2radians with respect to the second phase φ₂. The phase splitter 217 mayfor example output the first signal LO(φ₁) at a first output connectedto an input of a first mixer 214 and output the second signal LO(φ₂) ata second output connected to an output of a second mixer 215.

The mixers 214,215 may mix the filtered signal S_(f) with the first andsecond local oscillator signals LO(φ₁), LO(φ₂) respectively. Thereby,respectively an in phase (I) signal and an out-of-phase signal (e.g. aquadrature (Q) signal in case of a phase difference of π/2 radians) maybe obtained. The mixers 214,215 may output the respective mixed signalsto a combiner which combines the first signal LO(φ₁) and second signalLO(φ₂) into the, modulated, output signal S_(rf).

As shown in FIG. 1, the modulation unit 21 may be connected with anoutput 219 to an input 220 of a power amplifier 22. The power amplifier22 may receive a modulated signal S_(RF), for instance a signalgenerated by the example of a modulation unit 21 shown in FIG. 2. Thepower amplifier 22 may amplify the inputted signal and output theamplified signal to an output 23 of the transmitter 2, for instance viaan antenna 4 or other suitable output device. In the example of FIG. 1,the transmitter 2 is an wireless transmitter and, via the antenna 4,wireless signals may be outputted. More in particular, the transmitteris a transmitter of RF signals and via the antenna 4 electromagneticwaves may be outputted.

FIG. 8 schematically illustrates a 3π/8-PSK method. As shown in FIG. 8,the phase of the signals is shifted corresponding to the symbol (0,1,2 .. . 7). After the (thus phase shifted) signal is outputted the mappingof symbols is rotated with an additional phase shift of +3π/8 radians,for each transition from a current symbol to a following symbol. Forinstance, supposing the current symbol is 0, corresponding to a phaseshift of 0 (and to a binary sequence of 0,0,0), and the next symbol is1, corresponding to a phase shift of π/4 (and to a binary sequence of0,0,1), the signal will be phase shifted with 3π/8+π/4=7π/8 radians. Thefirst predetermined data sequence T1 of: and the second predetermineddata sequence T2 may for example be selected from symbol sequenceslisted in Table 4

TABLE 4 T1 T2 7214 70431625 6305 62570431 5630 57043162 4721 431625703056 31625704 2147 25704316 1472 16257043 0563 04316257

It is found that when modulated with 3π/8-PSK method such a symbolsequence result in a modulated signal with distinct frequencycharacteristics which allow an accurate testing of the components 21,22of the transmitter 2.

The invention may also be implemented in a computer program for runningon a computer system, at least including code portions for performingsteps of a method according to the invention when run on a programmableapparatus, such as a computer system or enabling a programmableapparatus to perform functions of a device or system according to theinvention. Such a computer program may be provided on a data carrier,such as a CD-rom or diskette, stored with data loadable in a memory of acomputer system, the data representing the computer program. The datacarrier may further be a data connection, such as a telephone cable or awireless connection. Such a computer program may for example be used tosimulate the performance of one or more components of a transmitter orto test a design of such components.

In the foregoing specification, the invention has been described withreference to specific examples of embodiments of the invention. It will,however, be evident that various modifications and changes may be madetherein without departing from the broader spirit and scope of theinvention as set forth in the appended claims. For example, othermodulation schemes may be used. Furthermore, the test unit 1 may be usedto test transmitters that may be used in a telecommunication system,such as a mobile telephone network or any other suitable type of network

Also, the invention is not limited to physical devices or unitsimplemented in non-programmable hardware but can also be applied inprogrammable devices or units able to perform the desired devicefunctions by operating in accordance with suitable program code.Furthermore, the devices may be physically distributed over a number ofapparatuses, while functionally operating as a single device. Forexample, the modulation unit 21 may be implemented as two or moresemiconductor devices and include a separate local oscillatorimplemented on a different piece of semiconductor than e.g. the mappingunit.

Also, devices functionally forming separate devices may be integrated ina single physical device. For example, the modulation unit 21 and/or thepower amplifier and/or the antenna 4 may be implemented in a singleintegrated circuit package.

However, other modifications, variations and alternatives are alsopossible. The specifications and drawings are, accordingly, to beregarded in an illustrative rather than in a restrictive sense.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. The word ‘comprising’ does notexclude the presence of other elements or steps then those listed in aclaim. Furthermore, the words ‘a’ and ‘an’ shall not be construed aslimited to ‘only one’, but instead are used to mean ‘one or more’, anddo not exclude a plurality. The mere fact that certain measures arerecited in mutually different claims does not indicate that acombination of these measures cannot be used to advantage.

1. A test unit for testing frequency characteristics of at least onecomponent of a transmitter of modulated signals, comprising: a datasource for generating a test pattern of data; a test unit outputconnected to said data source and connectable to an input of said atleast one component, to input said test pattern of data to said at leastone component; and a memory to store a first predetermined data sequenceand a second predetermined data sequence; wherein said data source isconnected with an data input to said memory, and said data source isarranged to generate said test pattern of data including said first andsecond predetermined data sequences; and wherein when a modulated signalis generated in accordance with said test pattern of data, the modulatedsignal includes a first signal part with a first frequency spectrumcaused by said first predetermined data sequence and a second signalpart after said first signal part, wherein second signal part has asecond frequency spectrum caused by said second predetermined datasequence.
 2. A test unit as claimed in claim 1, further including: areceiving unit connectable to said at least one component, for receivinga signal outputted by said at least one component in response toinputting said test pattern in said at least one component.
 3. A testunit as claimed in claim 1, wherein said first signal part and saidsecond signal part are modulated signals, said first signal part havingat least one frequency component with a first frequency above a carrierfrequency with a higher intensity than a corresponding frequencycomponent in the second signal part, and said second signal part havingat least one frequency component with a second frequency below saidcarrier frequency with a higher intensity than a corresponding frequencycomponent in the first signal part.
 4. A test unit as claimed in claim3, wherein said frequency component of the first signal part is a firstupper side band of the modulated signals above the carrier frequency andwherein said frequency component of the second signal part is a firstlower side band of the modulated signals below the carrier frequency. 5.A test unit as claimed in claim 3, wherein said first signal part andsaid second signal part each exhibit a frequency spectrum of asingle-sideband modulated signal.
 6. A test unit as claimed in claim 1,wherein a signal source is arranged to generate a phase modulatedsignal.
 7. A test unit as claimed in claim 6, wherein said first datasequence includes at least two different symbols and wherein atransition between two successive symbols corresponds in said firstsignal part with a first phase shift in a first direction, said seconddata sequence includes at least two different symbols, and a transitionbetween a symbol to a following symbol corresponding to a second phaseshift in a second direction opposite to said first direction.
 8. A testunit as claimed in claim 7, wherein said first data sequence and saidsecond data sequence each include at least three symbols and whereinsaid first and second phase shifts have a same magnitude for eachtransition from the symbol to the following symbol.
 9. A test unit asclaimed in claim 7, wherein said first and second phase shifts are in arange of larger than zero and smaller than 180 degrees.
 10. A test unitas claimed in claim 1, wherein a signal source is a source of m-PSKmodulated signals with a phase offset of pπ/q radians, and wherein m isan integer number and m, p, and q satisfy a relationship:${{2{\pi\left( {\frac{n}{m} + \frac{p}{q}} \right)}} \neq {k\;\pi}},$ inwhich relation n is a positive integer number smaller or equal to m, andk is an integer number.
 11. A test unit as claimed in claim 1, wherein asignal source is a source of 8-PSK modulated signals with a 3π/8 offset,and said first data sequence and/or said second data sequence areselected from a group of symbol sequences consisting of: 7214, 6305,5630, 4721, 3056, 2147, 1472, 0563, 70431625, 62570431, 57043162,43162570, 31625704, 25704316, 16257043, and
 04316257. 12. A test unit asclaimed in claim 1, wherein a signal source has a burst mode to outputat least one signal burst and wherein said signal source is arranged tooutput said first and second signal parts in a same signal burst.
 13. Atest unit as claimed in claim 1, wherein a signal source includes a dataprocessor for assembling a data packet which includes said test pattern.14. A test unit as claimed in claim 13, wherein said data processor isarranged to include said test pattern in a part of the data packetselected from a group consisting of: tail, data, mid-amble, and guard.15. A test unit as claimed in claim 1, wherein said test pattern of dataincludes compensating data to compensate for an effect on a parameter ofa test signal, wherein the effect on said parameter is caused by thefirst predetermined data sequence, the second predetermined datasequence, or the first predetermined data sequence and the secondpredetermined data sequence.
 16. A transmitter unit including the testunit as claimed in claim
 1. 17. A method for testing a frequencybehaviour of at least one component of a transmitter of modulatedsignals, comprising: generating a test signal from a test pattern ofdata, wherein the test pattern includes a first predetermined datasequence and a second predetermined data sequence, and wherein the testsignal includes a first signal part with a first frequency spectrumcaused by said first predetermined data sequence, and a second signalpart with a second frequency spectrum caused by said secondpredetermined data sequence; and inputting said test signal in said atleast one component.
 18. A component of the transmitter tested with amethod as claimed in claim
 17. 19. A non-transitory computer programproduct loadable in a memory of a programmable apparatus, wherein thecomputer program product includes program code portions for executing amethod as claimed in claim 17 when run by said programmable apparatus.